An overview of the usefulness and uncertainties of immunoassays in environmental and occupational lung diseases was presented. Information is presented on immunoassays of potential diagnostic value in immunologic lung diseases, lung disease due to reactive chemicals, examples of lung diseases due to inhaled agents, examples of inhaled substances producing immunologic lung disease, animal models used to confirm the immunopathogenesis of trimellitic- anhydride (552307) (TMA) pulmonary disease, and factors related to antigen and host or cohort. While the potential exists for defining other diseases as clearly as the model of TMA immunologic lung diseases, some of the variables that complicate this type of investigation are discussed. These include the possibility that the antigen is also an irritant, that the antigen cannot be measured in the environment, and that the antigen is present in the workplace and at home. Several factors related to the host or cohort also complicate the process. These include cigarette smoking, the presence of irreversible obstructive lung disease, coincidental allergic or nonallergic asthma, misinformation, fear, and compensation neurosis.